In this blood smear from a pancytopenic dog (non-regenerative anemia, neutropenia, thrombocytopenia), there are several large blasts. In addition an unusual mononuclear cell with ruffled borders is seen (arrow) alongside a giant platelet (dysplastic; arrowhead). The mononuclear cell with ruffled borders is not truly blast but is a dysplastic megakaryocyte, called a micromegakaryocyte. The presence of the micromegakaryocyte and dysplastic large platelet in a dog with circulating blasts and pancytopenia is compatible with a diagnosis of acute megakaryoblastic leukemia, i.e. a leukemia that is differentiating down the megakaryocytic lineage. This is a rare form of leukemia in dogs.
